Pimco's Scott Mather is sticking to his prediction that the Federal Reserve will start raising interest rates this summer.

"They'll be moving very slowly, not in a mechanical fashion, up to probably a neutral policy rate that's around 2 percent," said Mather, the firm's chief investment officer in charge of U.S. core strategies.

"That's probably the best way to prolong the expansion."

Mather, speaking ahead of the Fed's statement Wednesday, told CNBC's "Power Lunch" that there will be no "apocalyptic" scenario when the central bank lifts off from zero interest rates.

He believes the Fed "will sort of indicate that the costs and risks of staying at zero are greater than the costs and risks of … beginning to normalize interest rates."